An oxidation/reduction (redox) process involves a transfer of electrons between one medium or compound and another medium or compound. The medium that loses or donates the electrons is oxidized in the process. The medium that gains or accepts the electrons is reduced in the process. A redox process can be a single step process in which a medium A accepts electrons from a medium C. Alternatively, a redox process can be a multistep process in which a medium A accepts electrons from a medium B, which in turn accepts electrons from a medium C. The net redox reaction being a transfer of electrons from medium C to medium A.
Oxygen can have undesirable effects on many products. For example, oxidation can cause degradation such as corrosion, or in the case of food products, oxidation can result in spoilage or discoloration. Oxygen absorbers or scavengers are often used in commercial product packaging to remove oxygen from an environment in an effort to minimize oxidation, e.g., to preserve food or medical products. Powdered iron is commonly used in commercial oxygen absorbers because it is relatively inexpensive and readily combines with oxygen at relatively low temperatures in the presence of a promoter to form iron oxide, i.e., rust.
However, iron is not suitable for all applications. While relatively inexpensive, it is still too costly in some instances. Moreover, some applications use metal detectors to identify contaminants, and iron cannot be used because it triggers these detectors.
U.S. Pat. No. 5,977,212 describes an ascorbate salt based oxygen scavenging composition with catalytic amounts of a first-row, transition metal compound such as an organic or inorganic compound of iron or copper. The composition is supported on a high surface area, microporous particulate material that has been impregnated with the composition. The carrier can be a polymer matrix, a film or mat (woven or non-woven), or a moisture permeable pouch or sachet which contains the supported oxygen scavenging composition. The '212 Patent describes an oxygen scavenging composition that includes about 1 part ascorbate and small amounts of Cu2+ supported on about 5 parts silica. This composition is then mixed with plastic, e.g., PVC, resin and formed into package films.
U.S. Patent Publication No. 2005/0205840 describes an oxygen scavenging system that includes laccase enzyme, a compound that serves as a reducing agent, and a functional barrier permeable to oxygen. Laccase enzyme is capable of accepting electrons from many known reducing agents, and transferring those electrons to reduce oxygen to water. Butylated hydroxyanisole, butylated hydroxytoluene, tertiary-butylated hydroquinone, ascorbic acid (and its salts) and iso-ascorbic acid (and its salts) are said to be the preferred reducing agents for the laccase. The system can also include a support material for the composition, such as wood pulp filter paper, glass fiber filter paper, paperboard, fabric, nonwoven fabrics, polymer films and label stock, polymeric materials, a mat, a card, a disk, a sponge, and polymeric foam. There is no suggestion that any of these materials participate in the reaction.